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Jared Medina, Steven A. Jax, Sashank Prasad, H. Branch Coslett; Role of visual guidance in reaching after right intraparietal sulcus resection. Journal of Vision 2010;10(7):1086. doi: 10.1167/10.7.1086.
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We report data from a 50-year-old woman (KH) who exhibited gross visually-guided reaching errors shortly after surgical resection of a benign brain tumor restricted to the right posterior intraparietal sulcus. Testing was performed two to three months post-resection. In Experiment 1, we assessed KH's ability to reach to non-foveated targets presented on a touch screen with either the right or left hand. Trials were randomly presented within two conditions: with vision during the entire reach, or without vision (using PLATO occlusion glasses) after reach initiation. KH was significantly less accurate with both hands when reaching for targets presented left but not right of fixation (non-foveal optic ataxia), and only on trials with vision of the limb. These results suggest that the right posterior intraparietal sulcus is involved in online correction of visually-guided reaching. Second, previous studies reported that optic ataxics became more accurate when reaching to remembered target locations when compared to visible target locations (e.g. Milner, Paulignan, Dijkerman, Michel, & Jeannerod, 1999; Milner et al., 2001; Himmelbach & Karnath, 2005). In Experiment 2, we repeated the same task as in Experiment 1, with a five second delay between stimulus offset and reach initiation. In contrast to this previous report, KH was significantly less accurate when reaching to targets after a five second delay (relative to visible targets). We discuss our findings with respect to the neural representations used to guide reaching to visible and remembered target locations.
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